Single-probe Near-field Phase Retrieval using On-The-Fly Scan and Hilbert Transform

A novel near-field measurement method is proposed for fast phase retrieval using a single probe. The method is based on a new understanding of the on-the-fly (OTF) scan process as a spatio-temporal sampling operation of near-field responses. As a result, the near-field measurement is interpreted as a signal modulation of a source signal and a variable spatio-temporal function defined by the field responses and the motion of the probe. To retrieve the complex field responses, the Hilbert Transform (HT) is utilized for envelope and phase demodulation of signals recorded by an oscilloscope. To demonstrate the proof of concept, both numerical and experimental examples are provided with a detailed description of the method implementation. Measurement-to-measurement correlations at 125 kHz are conducted using a six-axis industry robot with multiple probes and instruments, showing its efficiency, effectiveness, and flexibility. Compared to conventional near-field measurement methods, the proposed method allows 90% reduction of measurement time and achieves a relative accuracy of phase retrieval above 96% with a simplified measurement setup, opening up new opportunities for near-field measurement applications.